1. Field of the Invention
The present invention, in general relates to woodworking tools and, more particularly, to a guide for use along with a router in the cutting of a dado.
Routers are used to make dado cuts, which are essentially channels, in boards for shelves and other similar purposes. The finished dado cut is also sometimes referred to as merely a “dado”. It is important to make the dado cut precisely where desired to prevent damage to the board and also to ensure that all parts align, for example, that both sides of a shelf are parallel. This requires precise location of each dado cut on each side of the shelf.
Prior types of devices used to help make a dado cut with a router are generally referred to as “dado guides”. However, prior types of dado guides have certain disadvantages. For example, one such type of product that is available from Accurate Woodworking Tools, LLC, 6991 Hollander Lane, Pickett, Wis., 54964, is referred to as their model “ACCURATE GUIDE”.
It relies on a fixture (i.e., the guide portion) that slides along adjacent to a fence. The fence is clamped onto a board to be cut (also sometimes referred to as a “work-piece”) and the fixture is attached to a router by rods that extend away from the fixture. Accordingly, the router is disposed the width of the fixture plus the length of the rods away from the fence.
Two cuts are generally required for each dado cut that is made on each board. This is because the width of the dado-cut usually exceeds the width of the router bit that is making the cut. Therefore, multiple passes of the router and router bit are required in order to make the dado cut. The first pass is made with the fixture adjacent to the fence. Subsequent passes will require that the router be offset further away from the fence.
The first pass is itself, difficult because there is often no mechanism that ensures the fixture will stay adjacent to the fence. Accordingly, the fixture can pull away from the fence if the user is not careful. One moment of inattentiveness and the board is ruined.
However, there is another substantial disadvantage that occurs when the router is disposed a substantial distance away from the fence. This disadvantage remains true for the first and also for the second or all subsequent passes.
The distance that the router is disposed away from the fence produces a moment arm when pushing on the router longitudinally with respect to the fence. Accordingly, torque is produced that attempts to twist (i.e. rotate) the fixture relative to the fence (i.e., the router experiences a force that is urging it to rotate about the moment arm and to move in closer toward the fence). Absent a mechanism to hold the fixture in position proximate the fence, the fixture can rotate, thereby skewing the cut that is being made and again ruining the board.
It is especially important to understand that this phenomenon of torque, while related to the distance the router is disposed away from the fence, has a critical limit. If the router is held so that its center is within a few inches of the edge of the fence, almost all of the force that is applied to urge the router and dado guide longitudinally along the length of the fence is used for that purpose. Very little torque is produced and very little binding occurs.
However, when the router is disposed a few more inches away from the fence, considerable torque and binding can occur. Therefore, it is not necessary—nor is it even possible—to dispose the router directly over the fence. It is a substantial improvement over the known prior art to dispose the router sufficiently close to the fence so as to minimize the moment arm below a critical point that produces noticeable binding.
If the prior art dado guide fixture is of a type that is adapted to engage with a fence (i.e., to surround a portion of the fence on both sides), then the torque that is produced tends to bind the fixture relative to the fence, making it especially difficult to urge the router along the longitudinal length of the fence.
The greater the distance the router is disposed away from the fence, the greater will be the moment arm that is produced and, accordingly, the greater will be the torque (i.e., the moment arm) that is generated and, therefore, the greater will be the binding of the fixture to the fence. As greater force is applied to the router to urge it along the longitudinal length of the fence, the greater is the likelihood that slippage can occur, thereby damaging the work-piece or possibly even exposing the user to possible injury. Also, the more force that is applied to a prior art type of router or dado guide fixture, the greater in turn will be the binding that results, due to the long moment arm.
Another disadvantage with prior art fixtures (i.e., various types of dado guides) is that the attachment of the router to the fixture produces a relative, changing, and unpredictable distance between the two. It depends on how deep the rods are attached to the fixture and how deep the rods are inserted into the base of the router itself. There is no fixed or minimum distance from the router bit to any portion of the fixture. Accordingly, there is no way to determine exactly where the dado cut will actually occur in the board (work-piece). Careful measurement is required which, at best, provides a guess as to where the dado cut will occur.
A further disadvantage of the prior art devices is that after the first cut necessary to make the dado cut has been made, then a piece of scrap wood from the shelf or board that will eventually be placed into the dado cut must be inserted into the fixture to introduce a further offset in the position of the router and router bit relative to the fence sufficient to displace the router bit further away from the fence an amount that is equal to the thickness of the board that will be inserted into the dado cut.
There are numerous disadvantages with this approach, let alone the most obvious disadvantage that there may simply not be a scrap piece of wood available if the entire length of the board that is placed in the dado cut is to be used. For example, a person can purchase several three foot long shelves, already cut, and plan on using them to make a bookcase. There are no scrap pieces available in this instance. If a portion of one of the shelves is used, then that entire shelf may become scrap, thereby increasing cost and waste.
Assuming that scrap material is available and that the prior art type of fixture can be set for the second pass (i.e., the second cut necessary to complete the dado cut), the cutting operation must then be interrupted (i.e., stopped) in the middle of each dado cut that is being formed and the fixture adjusted prior to finishing the dado. This is especially time consuming to accomplish for each dado cut that is to be made. Remembering that if four or five shelves are to be used then eight to ten dado cuts will be required, each of which will require this stoppage and additional calibration step to occur before completion of that particular dado cut can occur.
It is also useful to note that sometimes two passes (i.e., cuts) may not be enough to fully form the dado cut if an especially wide shelf is being used or if the router bit is especially tiny. It is desirable for the dado guide fixture to define both the inside pass (i.e., an inside edge of the dado cut) and the outside pass (i.e., an outside edge of the dado cut).
Then, with a prior art type of device, the user can make additional passes as needed to carefully remove the inner remaining material from the dado cut. However, unless the dado guide is able to limit the range of motion that the router can experience that is either closer to or further away from the fence, the danger is that the user may slip and move the router either too close or too far away from the fence, thereby damaging or ruining the work-piece (i.e., the shelf).
Or, with certain other prior art device, the operation must again be stopped during each dado cut and the fixture reset so that a third setting can be made to remove some of the remaining material from the dado cut. Again, if the shelf is especially wide or if the router bit is small, several such stoppages and additional settings may be required to fully remove all of the material from each dado cut.
Second, the scrap wood must be inserted into a particular slot of certain prior art devices depending upon the size of the router bit and the thickness of the dado cut. If the scrap wood is inserted in the wrong slot, which is entirely possible, then too large a dado can be produced, thereby ruining the entire board (work-piece).
Since the board that is having the dado cuts made therein is usually a side of a bookcase or other large piece of furniture, it tends to be the most expensive part of the bookcase or other type of furniture. This is often true because the board tends to be large and also because an entire exterior of it is often visible. Therefore, a high grade of material is often used. This makes it especially exasperating to damage the work-piece. Also, if several dado cuts are being made in the board, it is indeed quite exasperating for a fixture-related problem to ruin the work-piece while making one of the last of the required dado cuts.
Third, after this adjustment has been made with the prior art device, and a second pass (cut) is to be made, the router is thereby displaced in such a manner as to include an offset with respect to that portion of the dado cut that has already been made in the board. If the dado extends from end to end of the board, then the next pass (i.e., cut) can be made from beyond one end of the board extending past the other end and using the same router bit.
However, certain types of dado cuts do not extend from end to end of the board, Rather, they are contained within the board (i.e., they do not extend to the ends of the board). This type of a dado cut is sometimes referred to as a “stop dado” or “stop dado cut” because it extends across the board for an amount and then stops before an end or both ends of the board are reached.
When making a stop dado cut, after having made a first pass and after having reset the fixture so as to displace the router and router bit further away from the fence, the new cutting position of the router bit will interfere with the wood. It will not be possible to place the router fully down into the fixture without having to remove some of the remaining wood from the dado cut. In order to accomplish this, a further changing of router bits (to a new bit that can cut on its bottom) in order to penetrate the wood will likely be required. The wood will then need to be penetrated with the “end cutting” type of router bit from the top down in order to expand the size of the dado cut sufficient to accommodate the router bit and allow placement of the router fully down again into the fixture. After the “plunge cut” into the board has been made it is likely that a changing back to the original router bit (that cuts on its circumference, but not its bottom) will be required to finish the stop-dado type of cut. These router bit changes greatly extends time to complete each stop dado cut.
Clearly, it is desirable to provide a dado guide that will allow any number of subsequent passes to occur when making stop dado cuts that can all be accomplished with the same, side or circumferential-type of router bit, thereby eliminating the need for additional plunge-cuts.
There is another problem associated with the use of routers making two (or more) passes to form a dado cut. The first pass is typically made in a first direction and the second pass is typically made in an opposite second direction. In one direction the router bit itself is rotating in a direction that tends to pull the router toward the fence and in the opposite direction, the router bit will tend to urge the router away from the fence. Motion in either direction can ruin the board that is being cut. This is difficult, especially for unskilled users, in that sufficient skill and anticipation of the router-created forces have not yet been well-developed.
Additionally, certain prior art devices may include detachable parts, like pins, that can easily be lost or misplaced. It is desirable to provide a dado guide that does not include small detachable parts.
Additionally, it is also desirable to be able to set the desired width of a dado cut as quickly as possible. Prior art devices that use replacement shims or templates or which rely on the loosening of a locking type of screw are time-consuming and difficult to set. Such devices require moving a part after the screw has been loosened, and then tightening the screw to secure the adjustable part in the desired new position or with the new shim or template in position. There is also the possibility that the part that has been moved can shift position before the screw is once again fully tightened, thereby resulting in a dado cut that is either too wide or too narrow.
Accordingly, there is a need to be able to quickly set the width of a dado cut.
There is also a need to readily and precisely determine an edge of the dado cut. If a dado cut is not made at a precise location, then the shelves that extend across the two boards will not be level. This too can potentially ruin one or both of the work-pieces.
Similarly, there is a need for a dado guide that can be quickly set to accommodate different sizes of fences. Different users have different fences. There is not a uniform universal standard for the size of fences. Therefore, an ideal dado guide would permit adjustment sufficient to accommodate a variety of different sizes of fences.
Also, as mentioned above, sometimes a dado-cut will not pass entirely across the board thereby requiring that a “stop-dado” or “stop-dado cut” be made. It is difficult with prior art devices to determine where to stop longitudinal movement of the dado guide (and router) along the fence in order to end the stop dado cut exactly where the “stop” is required to occur. Accordingly, there exists a need to readily determine a stop position for a dado cut.
Also, there are a couple of sizes of router bits that are most commonly used to form a dado cut. This is simply a matter of mechanical engineering in that the width of most boards (i.e., shelves) will be greater than about three-eighths of an inch in order to provide sufficient load-bearing capability. This is true whether the shelf is made of wood or some other material, such as glass.
Accordingly, the two most common router bit sizes for use in forming dado cuts are three-eighths of an inch in diameter and one-half of an inch in diameter. It would also be especially desirable for a router guide to accept these two sizes of router bits with minimum adjustment and, after such minimum adjustment had been accomplished, to provide clear indication as to where an edge of the resultant dado cut that is to be made will occur.
It is important to note that all shelves are not made of wood. If a glass shelf is to be inserted into the dado cut, that further compounds the problems mentioned hereinabove that appertain to the known prior art devices. For example, it is not practical to provide a scrap piece of the glass shelf for calibration of the width of the dado cut that is required. Neither is it possible to hold a large piece of glass in a prior art type of dado guide during the actual formation of the dado cut.
Accordingly, there exists today a need for a dado guide that helps ameliorate these and other disadvantages.
Clearly, such an apparatus would be a useful and desirable device.
2. Description of Prior Art
Dado guides are, in general, known and are similar to the above-described device available from Accurate Woodworking Tools, LLC. In general, the router is displaced away from a fence and produces substantial torque when pushed. The cutting procedure for each dado must be interrupted (i.e., it cannot be a continuous operation). Scrap boards are required to adjust the cutting width. And a lack of precision in setup as well as location of the actual dado is inherent with all known prior art devices.
While the structural arrangements of the above described devices, at first appearance, may have similarities with the present invention, they differ in material respects. These differences, which will be described in more detail hereinafter, are essential for the effective use of the invention and which admit of the advantages that are not available with the prior devices.